// Adapted from Chris Veness' SHA1 code at
// http://www.movable-type.co.uk/scripts/sha1.html
function f(s: 0 | 1 | 2 | 3, x: number, y: number, z: number) {
  switch (s) {
    case 0:
      return (x & y) ^ (~x & z);
    case 1:
      return x ^ y ^ z;
    case 2:
      return (x & y) ^ (x & z) ^ (y & z);
    case 3:
      return x ^ y ^ z;
  }
}

function ROTL(x: number, n: number) {
  return (x << n) | (x >>> (32 - n));
}

function sha1(bytes: Uint8Array): Uint8Array {
  const K = [0x5a827999, 0x6ed9eba1, 0x8f1bbcdc, 0xca62c1d6];
  const H = [0x67452301, 0xefcdab89, 0x98badcfe, 0x10325476, 0xc3d2e1f0];

  const newBytes = new Uint8Array(bytes.length + 1);
  newBytes.set(bytes);
  newBytes[bytes.length] = 0x80;
  bytes = newBytes;

  const l = bytes.length / 4 + 2;
  const N = Math.ceil(l / 16);
  const M: Uint32Array[] = new Array(N);

  for (let i = 0; i < N; ++i) {
    const arr = new Uint32Array(16);

    for (let j = 0; j < 16; ++j) {
      arr[j] =
        (bytes[i * 64 + j * 4] << 24) |
        (bytes[i * 64 + j * 4 + 1] << 16) |
        (bytes[i * 64 + j * 4 + 2] << 8) |
        bytes[i * 64 + j * 4 + 3];
    }

    M[i] = arr;
  }

  M[N - 1][14] = ((bytes.length - 1) * 8) / Math.pow(2, 32);
  M[N - 1][14] = Math.floor(M[N - 1][14]);
  M[N - 1][15] = ((bytes.length - 1) * 8) & 0xffffffff;

  for (let i = 0; i < N; ++i) {
    const W = new Uint32Array(80);

    for (let t = 0; t < 16; ++t) {
      W[t] = M[i][t];
    }

    for (let t = 16; t < 80; ++t) {
      W[t] = ROTL(W[t - 3] ^ W[t - 8] ^ W[t - 14] ^ W[t - 16], 1);
    }

    let a = H[0];
    let b = H[1];
    let c = H[2];
    let d = H[3];
    let e = H[4];

    for (let t = 0; t < 80; ++t) {
      const s = Math.floor(t / 20) as 0 | 1 | 2 | 3;
      const T = (ROTL(a, 5) + f(s, b, c, d) + e + K[s] + W[t]) >>> 0;
      e = d;
      d = c;
      c = ROTL(b, 30) >>> 0;
      b = a;
      a = T;
    }

    H[0] = (H[0] + a) >>> 0;
    H[1] = (H[1] + b) >>> 0;
    H[2] = (H[2] + c) >>> 0;
    H[3] = (H[3] + d) >>> 0;
    H[4] = (H[4] + e) >>> 0;
  }

  // Note: Uint8Array.of() does `& 0xff` for each value
  return Uint8Array.of(
    H[0] >> 24,
    H[0] >> 16,
    H[0] >> 8,
    H[0],
    H[1] >> 24,
    H[1] >> 16,
    H[1] >> 8,
    H[1],
    H[2] >> 24,
    H[2] >> 16,
    H[2] >> 8,
    H[2],
    H[3] >> 24,
    H[3] >> 16,
    H[3] >> 8,
    H[3],
    H[4] >> 24,
    H[4] >> 16,
    H[4] >> 8,
    H[4]
  );
}

export default sha1;
